1. Field of the Invention
The present invention relates to a motor rotor and a method for making the motor rotor such that the rotor can be manufactured at a faster speed and that the rotor may rotate stably.
2. Description of the Related Art
Taiwan Utility Model Publication No. 341291 issued on Sep. 21, 1998 and entitled xe2x80x9cROTOR STRUCTURE FOR A FAN MOTORxe2x80x9d discloses a rotor that is made from plastic material by injection molding. For magnetic circuit requirement an integrally formed metal ring is provided on an inner periphery of the rotor and a magnet ring is fixed to an inner periphery of the metal ring. Since the metal ring is integrally formed with the rotor, the metal ring must be put into the mold for forming the rotor. In addition, the rotor must be formed with a central shaft at the same time. Thus, embedding of the metal ring and centering of the central shaft may slow down the overall formation speed of the rotor. In addition, in order to securely engage the metal ring with the rotor and to improve the strength of the metal ring to avoid deformation, the cross section of the metal ring must be in the form of an inverted L-shape with a flange on top side, yet this requires several punching steps and thus results in an increase in the cost for processing and material waste.
It is a primary object of the present invention to provide a motor rotor and a method for making the motor rotor such that the rotor can be manufactured at a faster speed and with a lower cost.
In accordance with the present invention, a rotor casing and a central shaft of the rotor are integrally formed by injection molding. A metal ring is mounted to a circular inner periphery of the rotor casing. The metal ring is formed by means of bending a strip of metal plate that has a length equal to or slightly smaller than an inner circumference of the rotor casing. Thus, the metal ring has certain resiliency to exert a radially outward force to the inner periphery of the rotor casing. In addition, two ends of the metal ring may contact with each other or have a gap therebetween. A permanent magnet ring is tightly fitted onto a circular inner periphery of the metal ring mounted in the rotor casing.
Other objects, specific advantages, and novel features of the invention will become more apparent from the following detailed description and preferable embodiments when taken in conjunction with the accompanying drawings.